DYNAMIC MODELING AND ANALYSIS OF LARGE-LOOP COUPLED BY ATTITUDE CONTROL AND POGO FOR LARGE LIQUID ROCKETS

Coupling effect always exists between structural vibration, attitude and propulsion system because of the spatial distribution characteristics of the structural vibration mode of large liquid rockets. The coupling model of attitude control-structure-propulsion system is derived to investigate the effects of the propulsion system on the stability of attitude control system. The coupling is based on mechanism that the effects of attitude control system on the attitude motion and structural vibration as well as the interaction of propulsion system and structural vibration. By including the coupling factors between the propulsion system, structural system and attitude control system, the large-loop coupling model can be used to investigate the coupling stability of the large-loop coupling system. Besides, the coupling model can be directly used for frequency-domain analysis and time-domain simulation for the non-singularity. Based on this model, the effects of the propulsion system parameters-pump gain and accumulator energy value to the stability of attitude control system are analyzed by frequency domain analysis and time domain simulation. The results show that the variations of parameters-pump gain and accumulator energy value not only result in the instability of structural vibration but also lead to the instability of attitude motion. It is concluded that it is necessary to take the effect of POGO loop into count in the design of attitude control system.